1. Field of the Invention
The present invention relates to the field of packaging and handling systems for the shipment, storage and handling of pellicles that are used for covering pattern masks during the manufacture of integrated circuits.
2. Description of the Background Art
Integrated circuits typically are manufactured in processes that utilize pattern mask imaging. When these processes involve projection printing of the pattern mask images, ultraviolet light is passed through the apertures of the pattern mask and is focused on a layer of resist that is coated on a substrate wafer. The light forms a pattern in the layer of resist that corresponds to the pattern mask, and the layer of resist is then developed to expose portions of the substrate to form a photoresist mask. Because the image of the pattern mask is brought into sharp focus on the photoresist layer surface, any contaminating particles present on the surface of the pattern mask are also brought into sharp focus on the surface of the photoresist layer, causing undesirable printing on the contaminating particle images in the resist layer. Printing of contaminating particle images on the photoresist layer often renders the photoresist mask useless, resulting in considerable economic waste.
To reduce the risk of particulate contamination of pattern masks, protective pellicles are generally used to cover the mask. Pattern mask pellicles include a transparent pellicle film that extends across a pellicle frame, and are mounted over respective patterns masks by a pellicle mounting device. The pellicle frame separates the pellicle film from the pattern mask by a distance sufficient to keep the images of contaminating particles that are located on the outer surface of the pellicle out of focus, so that the images of the contaminating particles will not be printed with the circuit pattern on the light sensitive layer of resist.
While a pellicle will prevent focusing of contaminating particles on the outer surface of the pellicle, contaminating particles within the interior of pellicle that fall onto the pattern mask will print out with the pattern and may render the resulting photoresist mask useless. Although pellicles can be manufactured essentially particle-free, subsequent packaging, shipment, storage and handling can cause particulate contamination of the interior of the pellicle.
One method for preventing particulate contamination of the interior of a pellicle during Packaging, shipment and storage, is to seal the pellicle along the lower edge of the pellicle frame with a complementarily shaped backseal sheet that is peeled away shortly before the pellicle is mounted over the pattern mask.
Pellicles typically are removed from their packaging with gloved hands, and the potential exists that the interior of a pellicle can become contaminated with particles during removal of a backseal sheet, and prior to mounting the pellicle over the pattern mask. Also, pellicles typically are quite awkward to hold with the hand. There thus is a risk that the pellicle will be dropped during handling prior to mounting, and the pellicle thereby contaminated or even damaged.
There remains a need for improved systems for packaging and handling pellicles.